1. Field of the Invention
The present invention relates to a pulsed power supply unit for generating excitation energy of a pulsed laser such as a copper vapor laser, an excimer laser and a carbon dioxide laser.
2. Description of the Related Art
FIG. 5 shows a conventional pulsed power supply unit, for example, disclosed in Japanese Laid-Open Patent Publication No. HEI-4-200281. In FIG. 5, the conventional pulsed power supply unit illustrated comprises a DC voltage source 1 for generating a DC voltage, a reactor 2 whose one end is connected to a positive output terminal of the DC voltage source 1, a switch 4 connected in parallel to the DC voltage source 1, a capacitor 5 whose one end is connected to the other end of the reactor 2, a discharge load 6 connected to the other end of the capacitor 5, and a control circuit 9 for turning the switch 4 on and off.
Operation of the conventional pulsed power supply unit will be described below.
When the switch 4 is switched off by the control circuit 9, a current flows from the positive output terminal of the DC voltage source 1 through the reactor 2 and the capacitor 5 to the discharge load 6, thereby charging the capacitor 5 up to reaching an output voltage value of the DC voltage source.
Once the switch 4 is switched on by the control circuit 9, a current flows steeply from the switch 4 to the discharge load 6. As a result, electrostatic energy stored in the capacitor 5 is inputted to the discharge load 6.
The discharge load 6 laser-oscillates inside thereof using the energy as an excitation source, thereby generating a laser output light in proportion to the energy inputted. When the switch 4 is switched off by the control circuit 9 after a completion of these operations, charging of the capacitor 5 begins again. These operations are repeated approximately some hundreds to some thousands times per second. The switch 4 is switched repeatedly with high voltages and a large amount of currents at high speed. Consequently, a semiconductor switch composed of a semiconductor device is used for the switch 4.
Since the conventional positive power supply is constituted as described above, a charging voltage value of the capacitor needs to be set highly precisely for stabilizing a laser output. In this regard, however, since the charging voltage value is determined by the accuracy in the output voltage of the DC voltage source, the DC voltage source should have a high voltage and a high degree of precision. Such a fact results in a large-sized power supply unit and a high cost.